The high germicidal activity of elemental iodine is well known, but its low solubility in water (1 part in 3,450 at 20.degree. C.) militates against its use in aqueous antiseptics. It is used in aqueous alcohol solution as tincture of iodine, but such preparations are not suitable for sterilizing surfaces, instruments, utensils etc. and when used as disinfectants on open wounds, cuts and abrasions, cause irritation and dicomfort due to the rapid evaporation of the alcohol and precipitation of the iodine. Moreover, such preparations cause undesirable staining of the skin or other surfaces with which they come in contact.
Cantor and Shelansky in 1951 discovered that certain surfactants had the property of complexing with elemental iodine to yield molecular aggregates or micelles which on dilution with water yielded the free iodine in a germicidally active form. Such complexes were termed `iodophors` and they have become important commercial disinfectants and sterilizing agents.
An inspection of the voluminous patent literature relating to iodophor compositions makes it clear that many surfactants are capable of solubilising iodine. Thus, quaternary ammonium compounds are disclosed for this purpose in British patent specification No. 625,676. (West Laboratories Inc.); long chain alkyl phenol-ethylene oxide condensates are the non-ionic surfactants employed in the compositions covered by British patent specification No. 950,954 (West Laboratories, Inc.), in U.S. Pat. No. 2,989,434, (G. A. Brost, F. Krupkin and F. Woodward) and in British patent specification No. 923,114 (W. C. Evans & Co.). Condensates of ethylene oxide and aliphatic ethers or glycols are the preferred non-ionic surfactants employed as iodine solubilisers in the compositions referred to in U.S. Pat. No. 3,326,806 (G. P. Dolby) and in Netherlands patent application No. 64.12604 (W. C. Evans & Co.). Anionic surfactants have also been employed as iodine solubilisers, for example, in the iodophor compositions featured in U.S. Pat. No. 3,650,966 (R. L. Bakka) and 3,240,711 (G. C. Wittwer).
Mixtures of surfactants have also been employed, e.g. the mixture of poly-(vinyl pyrrolidine) and ethoxylated nonyl alcohol in German Offen. 2,105,057 (A. Halpern).
Other publications which disclose iodine/surfactant combinations include: British patent specifications Nos. 703,091 (General Aniline & Film Corp.); 962,955 (Bendix Corp.); 1,004,282 (West Laboratories, Inc.); 1,066,437 (W. C. Evans & Co.); 1,167,743 (West Laboratories. Inc.); 1,293.407 (BASF Wyandotte Corp.); and 1,311,952 (Marles-Kuhlemann-Wyandotte.) Iodine/amine compositions are disclosed in British patent specification Nos. 1,186,177 (Diversey Development Ltd.) and 1,316,571 (Dipenidam Ltd.).
In general, non-ionic surfactants have been preferred since the germicidal action of iodophors formulated with them is less adversely affected by the hardness of the water used to dilute them for use.
For many purposes it is desirable that iodophors, when diluted to the concentration in which they are used, should not foam to any great extent and the minimising of the foaming propensity is frequently the reason for the choice of a particular surfactant or surfactant mixture even though the germicidal properties and/or storage stability may not be so good as might be achieved by similar compositions formulated with other surfactants. It is a feature of one preferred embodiment of the invention to which this patent relates that it provides iodophors which combine low foaming properties and a high degree of germicidal activity.
Not all the elemental iodine complexed in iodophor compositions is made available on dilution and it is a very desirable feature of such compositions that the ratio of available iodine (as determined by titration with standard thiosulphate solution) to total iodine should be as close to unity as possible without creating instability and that this ratio should not be reduced significantly on storage. The compositions to which this patent relates are characterized by a high ratio of available to total iodine and excellent storage stability. Furthermore they contain a greater percentage of both total and available iodine than the great majority of commercial iodophors.
The germicidal activity of elemental iodine, it is known, is enhanced at low pH, and iodophors are generally formulated with the addition of an acid. Because of its good anticorrosion properties and buffering action, phosphoric acid is particularly useful in this respect. In one embodiment of this invention, a mixture of sulphuric acid and phosphoric acid is used to control the pH at or near the optimum level.
Hitherto, it has been found that the germicidal action of diluted iodophors is due solely to the elemental iodine released and that the activity of iodophor disinfectants can be accurately predicted from the known activity of aqueous or aqueous/alcohol solutions of iodine of similar iodine concentration.
I have now found that the use of certain tertiary amine oxides as solubilisers or co-solubilisers confers a synergistic bacterial action on iodophor compositions to give formulations which are much more active against certain pathogens, particularly the acid fast bacteria, than any hitherto disclosed iodophor.
In addition, the use of certain low foaming surfactants with these tertiary amine oxides gives compositions which have desirable low-foaming properties.
A further advantage of the compositions to which this patent relates is that the tertiary amine oxide functions as a stabilizer as well as a synergistic solubilizing agent in combination with surfactants, and such compositions show a high and stable ratio of active to total iodine.